Digital Subtraction Angiography
Digital Subtraction Angiography
Digital subtraction angiography (DSA) is a diagnostic procedure that allows a physician to visualize blood vessels through use of contrast media and digital computer imaging.
Angiography is a technique of producing pictures (angiograms) of internal structures by introducing dye (contrast media) into the circulatory system that show up on x-ray film when tissue is exposed with x rays.
The difference between DSA and traditional angiography is that with DSA two digital pictures of the tissue are taken. The first is made before the dye is introduced. The second is made after the dye is injected. A computer then removes, or subtracts, certain structures in the first picture from those in the second picture. This leave an angiogram that shows only the blood vessels and omits surrounding or background tissues.
DSA is used to detect blood clots, tumors, and other blockages in blood vessels and some ducts. The procedure is also used to examine the health of blood vessels after coronary artery bypass or other vessel grafting operations. Sometimes other procedures are performed during a DSA such as inflating a small balloon in an artery to unblock it (angioplasty), placing a stent, or metal mesh to hold an artery open, opening a blocked bile or duct, inserting a drainage tube into a blocked kidney duct, and inserting a pacemaker device in the chest. During this time, the image serves as a guide to the physician performing the procedure.
DSA is not a risk-free procedure. Individuals who are allergic to iodine or iodine-containing foods such as shellfish may have an allergic reaction to the contrast medium. This reaction can be severe and may cause difficulty breathing, A sudden drop in blood pressure, loss of consciousness, tissue swelling, and other symptoms of anaphylactic shock. If DSA (or any other angiogram) is recommended, patients should inform their physician of any allergies to food and medicines. Also, since the contrast dye is removed from the circulatory system by the kidneys and excreted in urine, the dye may put an additional burden on poorly functioning kidneys. People with reduced kidney function should discuss this with their physician.
During digital subtraction angiography the individual lies on a table. Electrodes are placed on the chest to monitor heart health throughout the procedure. An x ray of the area is taken before the dye is injected. Next, a local anesthetic is injected into the skin at the site where the dye will be introduced. A thin tube is then inserted into the blood vessel, and the dye is injected. Additional x-ray pictures are then taken that show the dye in the blood vessels. The computer subtracts structures in the first picture from those in the second picture almost instantaneously, leaving an uncluttered picture of the blood vessels of interest. DSA without any additional procedures can take as little as 30 minutes. If additional procedures are needed, the time can stretch to 3 hours.
No special preparation is needed for a DSA alone. If other procedures are to be performed, the physician will give specific instructions on preparation.
After the DSA, the individual needs to lie still for about 6 hours to prevent bleeding. During this time the individual will be monitored for complications. Depending on the appearance of complications, health of the individual, and any additional procedures performed, an overnight stay in the hospital may be necessary.
In addition to allergic reactions to the dye, complications include damage to the artery by the tube used to inject the dye. In addition debris on the artery wall (plaque) can be dislodged by the procedure and block the artery. Blockage can cause stroke, heart failure, or tissue damage.
A DSA should provide a clear picture of the blood vessels of interest. Should the picture be inadequate to make a definitive diagnosis, other tests can be performed. These include a traditional (non-subtraction) angiogram, duplex sonography, or a magnetic resonance angiogram (MRA).
Health care team roles
DSA usually is most often performed in a hospital setting. The health care team includes at minimum a nurse to monitor heart performance, a radiology technician and a radiologist. Other team members are added if additional procedures are performed.
Contrast medium— Dye injected into the circulatory system that when exposed to x rays makes it possible to see blood vessels and other soft tissues.
Duplex sonography— Also called duplex ultrasound, this non-invasive procedure uses two different types of sound waves simultaneously to produce a picture of the structure of the blood vessel and the way blood is moving through it.
Magnetic resonance angiogram (MRA)— Similar to magnetic resonance imaging only enhanced by the use of contrast media.
Plaque— A mixture of fat, cholesterol, and cellular debris that builds up in the inner lining of an artery.
Modaresi, K.B., et al. "Comparison of intra-arterial Digital Subtraction Angiography, Magnetic Resonance Angiography and Duplex Ultrasonography for Measuring Carotid Artery Stenosis." British Journal of Surgery 85 (November 1999) 1422-1426.
American College of Radiology. 1891 Preston White Drive, Reston, VA 20191. (703) 648-8900. http://www.act.org.
"Digital Subtraction Angiography." Doncaster and Bassetlaw Hospitals NHS Foundation Trust. (undated). http://www.dbh.nhs.uk/our_services/medical_imaging/digital_subtraction_angiography.asp (November 23, 2005).